A. Field of Invention
This invention pertains to the art of fiber optics, and more specifically to fiber optic switches.
B. Description of the Related Art
It is known in the art to use electromagnetic switches to determine whether doors or panels are open or closed. On-off electromagnetic switches are also used as proximity or limit switches.
It is also known to use a fiber light pipe as an on/off switch. A light beam shines from a transmitter and is received by a receiver. If the receiver receives the beam, the switch is in one state, for example “on.” If the light beam is broken, the switch is in another state, for example “off.” However, because the light break occurs outside the fiber, the distance of such a switch is limited.
Also known is a measurement device that includes a fastener for use in attaching a first member to a second member, in which the fastener has an aperture extending through a length of the fastener, and a first optical fiber located within the aperture, in which the first optical fiber includes at least one fiber Bragg grating sensor. Such a device is described in U.S. Patent Pub. 2010/0329602, published on Dec. 30, 2010, entitled SMART FASTENER AND SMART INSERT FOR A FASTENER USING FIBER BRAGG GRATINGS TO MEASURE STRAIN AND TEMPERATURE (Shah, Chandler, Madsen, and Way), which is incorporated herein by reference.
Also known is a sensor apparatus that includes a resilient member positioned near a rod member and a strain sensor operatively connected to the resilient member. The rod member includes an eccentric member, which causes the resilient member to deflect as the rod member rotates. The strain sensor measures the strain in the resilient member due to the deflections caused by the eccentric member. The amount of strain relates to a rotational position of the rod member. Such an apparatus is described in U.S. Patent Pub. 2011/0011188, published Jan. 20, 2011, entitled FIBER OPTIC ROTATION/POSITION SENSOR (McNeilly), which is incorporated herein by reference.
What is needed, however, is an intrinsically-safe switch that can be used in hazardous environments and that can be located at a considerable distance from the equipment that receives the switch's signal. The present invention addresses this need.